C++ :

#include<bits/stdc++.h>
using namespace std;
long long d,s,a,b,x,y,tmp,ans;
long long f(long long a,long long b)
{
    if(a==0) return b;
    if(b==0) return a;
    long long c=a%b;
    while(c) a=b,b=c,c=a%b;
    return b;
}
int main()
{
    cin>>d>>s;
    for(long long x=1;x*x<=s;x++)
    {
        if(s%x!=0) continue;
        y=s/x;
        if((x+y)%2!=0 || abs(x-y)%2!=0) continue;
        a=(x+y)/2;
        b=abs(x-y)/2;
        if(f(a,b)==d) tmp=a,ans=max(ans,tmp);
    }
    if(ans>0) cout<<ans;
    else cout<<-1;
    return 0;
}